The present invention relates to a combination exhaust gas post treatment/muffler device in the exhaust gas section of an internal combustion engine, especially a diesel engine of a commercial vehicle such as a truck or bus, and includes a muffler, which is spatially delimited by a front and rear end wall as well as a peripheral outer wall, and in the interior of which is built in at least one preliminary oxidation catalytic converter, which significantly increases the amount of NO2 in the exhaust gas that is flowing through, and at least one, especially catalytic, particle separator, whereby exhaust gas that is to undergo post treatment can be introduced into the muffler via an inlet tube, and after flowing through the preliminary oxidation catalytic converter as well as the particle separator or separators can again be conveyed out of the muffler in a clean and indirectly muffled state.
In the following, the discussion concerns PM-KAT systems. PM-KAT® is a trademark of the applicant MAN Nutzfahrzeuge Aktiengesselschaft. PM-KAT systems refer to non-blocking means for reducing soot or carbon particles in the exhaust gas of diesel engines. Such PM-KAT systems comprise at least one preliminary oxidation catalytic converter, subsequently referred to as P-cat, the carrier of which is coated with platinum as the active component, and a downstream, especially catalytic, particle separator, subsequently abbreviated as PM separator. Such a PM separator, could, for example, have the configuration or structure disclosed in DE 100 20 120 C1. For trucks, an arrangement has been disclosed of a P-cat in a preliminary muffler that is disposed as close as possible to the internal combustion engine, and of one or more separators in the main muffler (see DE 101 23 358 A1).
In addition, the integration of the PM-KAT System in a commercial vehicle muffler was disclosed at the twenty-third International Viennese Motor Symposium on 25 and 26 Apr. 2002 and was documented in the Progress Reports, VDI Series 12 No. 490, Volume 2 Düsseldorf, VDI publication 2002, page 196–216. FIGS. 10 and 11 show this MP-KAT system of this literature citation. There it can be seen that disposed in the muffler 1 are four exhaust gas post treatment modules 2 for parallel flow therethrough, whereby each of the modules is encased in a casing 5 and is provided with a circular cylindrical P-cat 3 and following coaxially directly thereafter a circular cylindrical PM separator 4 having the same diameter. This integration of the PM-KAT system of the muffler 1 is provided when with a truck or bus there is no space for accommodating a preliminary muffler close to the engine. However, the drawback of this integration solution is a PM separator volume that is reduced by the volume of the P-cat, because the outer dimensions of the muffler 1 are dictated by the vehicle and can therefore not be increased. This leads to unsatisfactory separation rates of significantly less than 50%. Even an increase of the platinum concentration in the P-cat and an additional coating of the inner structures of the PM separator or separators would not lead to the goal of increasing the separation rate/conversion in the ETC (European Transient Cycle). Platinum is very expensive and therefore determines to a very considerable extent the cost of the overall system.
It is therefore an object of the present application, in a combination exhaust gas post treatment/muffler device of the aforementioned general type, to accommodate in the muffler a P-cat and PM separator having such a volume and such a shape and design that particle conversion rates of at least 50%, preferably, however, considerably greater than 50% in the ETC, can be achieved while using a minimum amount of platinum in the P-cat.